Tony Gazzo was a loan shark who employed Rocky Balboa before his boxing career took off in the first film. Rocky was a good club fighter, but his purses were often meager and insufficient to support his girlfriend Adrian, let alone himself. To augment his income, Rocky looked for whatever work he could, and caught the attention of Gazzo, who figured he could use Rocky as muscle. Rocky was responsible for collecting the debts, but in spite of his fearsome reputation, was reluctant to use violence outside the ring. Rocky once refused Gazzo's orders to break the fingers of one debtor, instead collecting a partial payment. When Gazzo angrily asked why Rocky failed to follow orders, Rocky protests had he broken the man's fingers, he would not have been able to work and earn the money to repay the rest of the debt. Gazzo, more concerned about reputation than collection, tells Rocky to "leave the thinking to me". Rocky's employment with Gazzo was also a bone of contention for Mickey, who banned him from his gym saying he had potential, but Rocky "fought like an ape" and his was a hired goon for "that loan shark".
Gazzo returns in the Rocky II, where he is one of the guests at the small simple wedding of Adrian and Rocky. When married life proves tough for Rocky, as he goes through a dry period of no work, Gazzo says his door is always open for Rocky as they are both of Italian ancestry, and Gazzo is obligated to help out. However, soon afterwards Apollo Creed announces his rematch with Rocky, and Rocky recommends his brother-in-law Paulie Pennino to do his old collection job. During the championship fight with Creed, Gazzo and his girlfriend are in the audience, and proudly cheer Rocky when he wins the belt.
Despite Gazzo being selfish, money hungry and sometimes downright criminal. Gazzo is also quite caring about Rocky, even lending him money so he can take Adrian out somewhere nice for the first date. He supported Rocky both times during his fights with Apollo and seems to be very proud of him, showing that Gazzo is not all bad.
In the Rocky IV novelization, it is revealed that Gazzo was killed by an unidentified culprit sometime before the events of the movie. His bodyguard, overcome with grief, committed suicide. However, the novelization was adapted from an earlier draft of the script, which differs significantly from the theatrical cut of the film. Nothing is ever mentioned about Gazzo beyond the second film.